A combination of washing with a chlorine-based disinfection detergent such as an aqueous solution of sodium hypochlorite and acid-washing with an aqueous acidic solution is generally carried out in washing medical instruments and facilities for producing medical preparations and foods. Pipes having an ultrafiltration membrane or a precision filtration membrane arranged therein for water treatment or the like, and these membranes, are washed by a combination of acid-washing with an aqueous acidic solution and alkali washing with an aqueous alkaline solution. Further, when medical instruments such as artificial hemodialysis instruments are disinfected and washed, sodium hypochlorite and acetic acid are known as the detergent used very frequently at present.
In particular, a chlorine-based disinfection detergent represented by sodium hypochlorite is used in a wide variety of applications such as washing of artificial hemodialysis instruments, etc. because of its strong sterilizing properties and its power to remove organic dirt such as protein and lipid.
Washing waste water using the chlorine-based disinfection detergent is desired to be disposed of after active chlorine is reduced to the minimum degree, from the viewpoint of its influence on the environment. With this background given, JP-A 64-11552 discloses a disinfection method that involves disinfecting an instrument as a subject of disinfection, with an aqueous solution of sodium hypochlorite and then adding a reducing agent to the aqueous solution to decompose sodium hypochlorite with the reducing agent. JP-A 10-235335 discloses that a reducing agent whose aqueous solution is alkaline is used as a treating solution to make a chlorine-based bleaching disinfectant harmless. On one hand, acid-washing using an organic acid such as acetic acid is carried out for the purpose of removing scale, but its waste water has a high BOD value, thus giving rise to concern about its influence on the environment, and may be hazardous because it can dissolve and destroy concrete buildings to cause a severe accident.